A radial roller bearing 1 as shown in FIG. 9 is incorporated in a portion of a rotational supporting portion of various mechanical apparatuses to which a large radial load is applied. This radial roller bearing 1 is provided so as to roll freely between an outer ring raceway 3 with a cylindrical surface that is provided on an inner circumferential surface of a radially outer member 2 such as a housing that does not rotate even in use (or a gearwheel or a roller that rotates in use) or the like and an inner ring raceway 5 with a cylindrical surface that is provided on an outer circumferential surface of a radially inner member 4 such as a rotational shaft (or a supporting shaft) or the like with a plurality of rollers (needles) 6 retained by a retainer 7 as shown in FIG. 10.
In these constituent parts of the radial roller bearing 1, the retainer 7 is fabricated integrally through injection molding using a synthetic resin and has a cylindrical shape as a whole. This retainer 7 includes a pair of rim portions (a one-end rim portion 8, the other-end rim portion 9) each having a circular ring shape that are disposed coaxially while being spaced away from each other in an axial direction and a plurality of pillar portions 10, 10 that are provided intermittently along the circumferential direction while being stretched between the one-end and other-end rim portions 8, 9. Portions that are surrounded around four sides by the pillar portions 10, 10 that lie adjacent in the circumferential direction and the one-end and other-end rim portions 8, 9 are made into pockets 11, 11 where to retain the rollers 6 individually. Retaining the rollers 6 within these pockets 11, 11 so as to roll freely therein, the retainer 7 is provided between the inner circumferential surface of the radially outer member 2 and the outer circumferential surface of the radially inner member 4 so as to rotate freely relative to the radially outer member 2 and the radially inner member 4. The retainer 7 rotates relative to the radially outer member 2 and the radially inner member 4 as the rollers 6 walk around.
In disposing the retainer 7 around the circumference of the inner ring raceway 5 to build up the radial roller bearing 1, the retainer 7 is placed on the radially inner member 4 from an end portion thereof and is further moved axially to the circumference of the inner ring raceway 5. As this occurs, however, in case an obstacle such as an outwardly oriented flange-like rib portion or the like with an outside diametric dimension that is larger than a bore dimension of the retainer 7 is present on the outer circumferential surface of the radially inner member 4 at a portion lying between the end portion of the radially inner member 4 and the inner ring raceway 5, this obstacle interrupts the passage of the retainer 7, whereby the retainer 7 cannot be moved axially to the circumference of the inner ring raceway 5.
Then, as a retainer that can solve the problem described above, for example, Patent Document 1 describes a retainer (a split retainer) in which a discontinued portion is provided at one location in a circumferential direction. FIGS. 11, 12A and 12B show a retainer 7a that is described in Patent Document 1. In this retainer 7a, a discontinued portion 12 is provided at one location in the circumferential direction. Additionally, an axial relative displacement of end portions (one circumferential end portion 13 and the other circumferential end portion 14) that are provided across the discontinued portion 12 is restricted (substantially prevented) through an engagement (a recess and projection engagement) between a first recess and projection portion 16 and a second recess and projection portion 17 that make up an engagement portion 15.
In the case of the retainer 7a having the configuration described above, the width of the discontinued portion 12 can be expanded in the circumferential direction by elastically deforming the retainer 7a. Because of this, the width of the discontinued portion 12 is expanded more largely than the outside diametric dimension of the radially inner member 4 such as a rotational shaft or the like to which the retainer 7a is assembled so that the shaft is passed through the discontinued portion 12, whereby the retainer 7a can be assembled to the circumference of the shaft. Alternatively, the bore dimension of the retainer 7a is elastically expanded to such an extent that the retainer 7a can ride over the obstacle, so that the retainer 7a is moved axially over the circumference of the shaft to thereby be assembled thereto.
In addition, in the case of the construction of the retainer 7a, as shown in FIG. 12A, in circumferential clearances between one circumferential end face 22 and the other circumferential end face 24 that are provided across the discontinued portion 12, a clearance Ha, Ha that aligns with (overlaps) the one-end rim portion 8a or the other-end rim portion 9a in relation to the axial direction is made larger than clearances Hb, Hc of other portions (Ha>Hb, Ha>Hc).
Incidentally, in this retainer 7a, a circumferential relative displacement of the one circumferential end portion 13 (the one circumferential end face 22) and the other circumferential end portion 14 (the other circumferential end face 24) is not restricted. Because of this, in case the retainer 7a is elastically deformed during operation, there may be a situation in which both the end faces 22, 24 are brought into strong abutment with each other.
FIG. 12B shows a state in which the circumferential clearance between both the end portions 22, 24 becomes the smallest in the construction of the retainer 7 described above. In this state, in the engagement portion 15, a front end face of a first engaging projecting portion 18 is in abutment with a deep end face of a second engaging recess portion 21, and front end faces of a pair of second engaging projecting portions 20, 20 are in abutment with deep end faces of a pair of first engaging recess portions 19, 19 (to bear a circumferential load).
These abutment portions are portions that correspond to axial intermediate portions of the pillar portions 10a, 10a that are provided at the circumferential one end and the other circumferential across the discontinued portion 12, and the circumferential rigidity is low at these portions. In case the circumferential load based on the abutment continues to be borne at the portions where the rigidity is low as described above in a repeated fashion, large stress is generated in these portions in a repeated fashion, damaging the portions, whereby the durability of the radial roller bearing retainer 7a is possibly reduced.
On the other hand, in contrast with the single-row retainer 7a that is described above, a double-row (a multi-row) retainer having a shape resulting from combining single-row retainers 7a in the axial direction can also be used to retain rollers that are aligned in a plurality (a multiplicity) of rows so as to roll freely.
FIG. 13A shows the construction of a retainer 109 that is described in Patent Document 1 as an example of a double-row retainer that makes up a radial roller bearing. This retainer 109 has a plurality of one-side pockets 110, 110 that retain, in rollers that are disposed in a plurality of rows, rollers in one row so as to roll freely and a plurality of other-side pockets 111, 111 that retain rollers in the other row so as to roll freely. Additionally, the retainer 109 has a discontinued portion 112 at one location in a circumferential direction. One circumferential end portion 113 and the other circumferential end portion 114 are brought into engagement with each other by an engagement portion 115 so as to prevent substantially an axial relative displacement of both the end portions 113, 114.
In the case of the conventional retainer 109 described above, the width of the discontinued portion 112 can be expanded in the circumferential direction by elastically deforming the retainer 109. This enables the retainer 109 to be assembled around a circumference of a radially inner member 4 (refer to FIG. 9) such as a rotational shaft or the line around which the retainer 109 is assembled by expanding the width of the discontinued portion 112 more largely than an outside diametrical dimension of the radially inner member 4 so that the radially inner member 4 is allowed to pass through a space in the discontinued portion 112. Alternatively, the retainer 109 can also be moved axially over the circumference of the radially inner member 4 to be assembled therearound by elastically expanding a bore diametrical dimension of the retainer 109 to such an extent that the retainer 109 can ride over an obstacle such as a step portion or an outwardly oriented flange-like rib or the like that is provided on the radially inner member 4.
The retainer 109, however, does not restrict a circumferential relative displacement of the one circumferential end portion 113 and the other circumferential end portion 114. Due to this, in case the retainer 109 is elastically deformed during operation, a circumferential space (clearance) between both the end portions 113, 114 changes, and in case the space decreases, there may be a situation in which distal end faces of both the end portions 113, 114 are brought into strong abutment with each other.
FIG. 13B shows a state in the construction of the retainer 109 described above in which the circumferential space between both the end portions 113, 114 becomes the smallest. In this state, both the end portions 113, 114 are brought into abutment with each other at the engagement portion 115 as follows; distal end faces of first engaging projecting portions 117a, 117b are in abutment with deep end faces of second engaging recess portions 120a, 120b, respectively, and distal end faces of second engaging projecting portions 119a, 119b are in abutment with deep end faces of first engaging recess portions 118a, 118b, respectively (a circumferential load is borne by the abutment portions).
These abutment portions correspond to axial intermediate portions of a one-side pillar portion and the other-side pillar portion 121, 122 at one circumferential end and axial intermediate portions of a one-side pillar portion and the other-side pillar portion 121, 122 at the other circumferential end, the pillar portions 121, 122 at the one circumferential end and the pillar portions 121, 122 at the other circumferential end being provided across the discontinued portion 12, and the abutment portions are portions where circumferential rigidity is low. In case the circumferential load based on the abutment continues to be borne repeatedly at the portions having the low rigidity, large stress is generated in those portions repeatedly, leading to a possibility that the portions bearing the load are damaged, whereby the durability of the radial roller bearing retainer 109 is reduced.